SPF, or Sun Protection Factor, refers to the increased, or lengthened, time to sunburn after the application of a sunscreen, compared to the time that it takes to burn with no sunscreen at all. For example, suppose that you burn in midday in 30 minutes. Under identical conditions, had you first applied an SPF 29 sunscreen, it would take 14.5 hours for you to experience a sunburn (29 x 0.5).

Remember also that ultraviolet light increases approximately 4% for every 1000 feet in altitude – so, in Denver, we have 20% more ultraviolet light, whereas at 10,000 feet we have 40% more UVL! Because of our outdoor lifestyle, with 300 days of sunshine per year, we have the highest rate of skin cancer in the nation!